In early January, says Freedman, a circulation pattern in the Arctic atmosphere known as the “polar vortex”—a strong circulation, moving counterclockwise, if you’re looking down at the North Pole, and located a few miles up in the air—began to break down. The strength of the polar vortex usually affects how much cold Arctic air is able to seep down to lower latitudes:

When there is a strong polar vortex, cold air tends to stay bottled up in the Arctic. However, when the vortex weakens or is disrupted, like a spinning top that suddenly starts wobbling, it can cause polar air masses to surge south, while the Arctic experiences milder-than-average temperatures.

At the beginning of the month, massive undulating waves in the Earth’s atmosphere known as Rossby waves, which usually trundle along in the lowest level of the atmosphere (the troposphere, where we live), managed to push their way into the next atmospheric level up—the stratosphere (where Felix Baumgartner jumped from a little while back). The effect of the Rossby waves on the polar vortex was that the vortex was “split in two.” The broken vortex caused the Arctic stratosphere to warm up suddenly and sent a bulge of frigid Arctic air flowing south.

Since cold air needs to make it all the way south and all the way down to the surface, says Freedman, usually there are a few weeks of lag between the suddenly warming Arctic stratosphere and cold temperatures further downstream.

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About Colin Schultz

Colin Schultz is a freelance science writer and editor based in Toronto, Canada. He blogs for Smart News and contributes to the American Geophysical Union. He has a B.Sc. in physical science and philosophy, and a M.A. in journalism.

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